1. Field of the Invention
This invention relates to gaskets made of fibers and methods of making the same. In particular, it relates to such gaskets for high temperature applications and which are made by spirally winding a fiber back on itself in a closed path to form a loop, with or without a core.
2. Background Information
Gaskets used for high temperature applications are commonly made of high temperature sleeving material. The limited selection of sizes of sleeving material available makes it difficult to accurately size the loop or toroidal-shaped gaskets needed for such application. An example of such a gasket is the gasket required to seal a ceramic filter safe guard device of precise geometry inside a metal container.
Large and sometimes irregularly shaped or custom contoured gaskets have required configuration of fabric into an elongated bundle (roll) which is joined at the ends by overlapping and stitching. A bulge, lump, hard spot, weak spot or other discontinuity is inevitably produced at the connection. This discontinuity may present a potential leak path and/or point of failure. An alternate technique of layering fabric and cutting it with loop shaped dies, and then stitching the fabric layers together, eliminates the overlap but presents the problem of frayed edges that are very susceptible to unraveling and deterioration at the gasket edges. An example of this type gasket is the rectangular shaped gasket needed to seal cross flow or sheet filters to their adjoining hardware. Back pulse cleaning of the filters further aggravates the problem of fraying with such a structure.
There is a need, therefore, for an improved gasket, especially for high temperature applications, but for other applications also, which can be easily fabricated to any desired shape, whether regular or irregular, with or without a core. In particular, there is a need for such an improved fiber gasket that does not have any weak spots, lumps, bulges, hard spots or other discontinuities.
These needs and others are satisfied by the invention which is directed to a loop gasket having a multi-layer spiral winding of a fiber back around itself in a closed path forming a loop. The multi-layer spiral winding can have a constant pitch so that the cross-section of the loop is substantially constant around the closed path. Alternatively, the multi-layer spiral winding of the fiber can have a variable pitch around the closed path so that the loop has a variable cross-section. Also alternatively, the gasket can have a core forming a loop on which the multi-layer spiral winding of fiber is formed. This core which may have various geometric configurations, can be made of strands of the fiber or a different material such as a stiff or rigid material or a resilient material. For high temperature applications, the fiber can be a ceramic fiber.
The invention also embraces the method of making a loop gasket comprising spirally winding a fiber back around itself along a closed path repetitively to form a loop. The fiber can be repetitively wound at a constant wrap rate around the loop to provide a uniform build up of gasket cross-section, or can be repetitively wound at a variable wrap rate around the loop to produce a variable gasket cross-section. The step of winding comprises forming the loop in a selected geometric form. Also, the fiber can be spirally wound on a core forming the loop. Again, for high temperature applications, the fiber can be a ceramic fiber. The loop can be of any geometric cross-section.